druid/docs/content/development/select-query.md

layout
doc_page

Select Queries

Select queries return raw Druid rows and support pagination.

 {
   "queryType": "select",
   "dataSource": "wikipedia",
   "descending": "false",
   "dimensions":[],
   "metrics":[],
   "granularity": "all",
   "intervals": [
     "2013-01-01/2013-01-02"
   ],
   "pagingSpec":{"pagingIdentifiers": {}, "threshold":5}
 }

There are several main parts to a select query:

property	description	required?
queryType	This String should always be "select"; this is the first thing Druid looks at to figure out how to interpret the query	yes
dataSource	A String or Object defining the data source to query, very similar to a table in a relational database. See DataSource for more information.	yes
intervals	A JSON Object representing ISO-8601 Intervals. This defines the time ranges to run the query over.	yes
descending	Whether to make descending ordered result. Default is false(ascending). When this is true, page identifier and offsets will be negative value.	no
filter	See Filters	no
dimensions	A String array of dimensions to select. If left empty, all dimensions are returned.	no
metrics	A String array of metrics to select. If left empty, all metrics are returned.	no
pagingSpec	A JSON object indicating offsets into different scanned segments. Query results will return a pagingIdentifiers value that can be reused in the next query for pagination.	yes
context	An additional JSON Object which can be used to specify certain flags.	no

The format of the result is:

 [{
  "timestamp" : "2013-01-01T00:00:00.000Z",
  "result" : {
    "pagingIdentifiers" : {
      "wikipedia_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9" : 4
    },
    "events" : [ {
      "segmentId" : "wikipedia_editstream_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9",
      "offset" : 0,
      "event" : {
        "timestamp" : "2013-01-01T00:00:00.000Z",
        "robot" : "1",
        "namespace" : "article",
        "anonymous" : "0",
        "unpatrolled" : "0",
        "page" : "11._korpus_(NOVJ)",
        "language" : "sl",
        "newpage" : "0",
        "user" : "EmausBot",
        "count" : 1.0,
        "added" : 39.0,
        "delta" : 39.0,
        "variation" : 39.0,
        "deleted" : 0.0
      }
    }, {
      "segmentId" : "wikipedia_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9",
      "offset" : 1,
      "event" : {
        "timestamp" : "2013-01-01T00:00:00.000Z",
        "robot" : "0",
        "namespace" : "article",
        "anonymous" : "0",
        "unpatrolled" : "0",
        "page" : "112_U.S._580",
        "language" : "en",
        "newpage" : "1",
        "user" : "MZMcBride",
        "count" : 1.0,
        "added" : 70.0,
        "delta" : 70.0,
        "variation" : 70.0,
        "deleted" : 0.0
      }
    }, {
      "segmentId" : "wikipedia_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9",
      "offset" : 2,
      "event" : {
        "timestamp" : "2013-01-01T00:00:00.000Z",
        "robot" : "0",
        "namespace" : "article",
        "anonymous" : "0",
        "unpatrolled" : "0",
        "page" : "113_U.S._243",
        "language" : "en",
        "newpage" : "1",
        "user" : "MZMcBride",
        "count" : 1.0,
        "added" : 77.0,
        "delta" : 77.0,
        "variation" : 77.0,
        "deleted" : 0.0
      }
    }, {
      "segmentId" : "wikipedia_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9",
      "offset" : 3,
      "event" : {
        "timestamp" : "2013-01-01T00:00:00.000Z",
        "robot" : "0",
        "namespace" : "article",
        "anonymous" : "0",
        "unpatrolled" : "0",
        "page" : "113_U.S._73",
        "language" : "en",
        "newpage" : "1",
        "user" : "MZMcBride",
        "count" : 1.0,
        "added" : 70.0,
        "delta" : 70.0,
        "variation" : 70.0,
        "deleted" : 0.0
      }
    }, {
      "segmentId" : "wikipedia_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9",
      "offset" : 4,
      "event" : {
        "timestamp" : "2013-01-01T00:00:00.000Z",
        "robot" : "0",
        "namespace" : "article",
        "anonymous" : "0",
        "unpatrolled" : "0",
        "page" : "113_U.S._756",
        "language" : "en",
        "newpage" : "1",
        "user" : "MZMcBride",
        "count" : 1.0,
        "added" : 68.0,
        "delta" : 68.0,
        "variation" : 68.0,
        "deleted" : 0.0
      }
    } ]
  }
} ]

The threshold determines how many hits are returned, with each hit indexed by an offset. When descending is true, the offset will be negative value.

The results above include:

    "pagingIdentifiers" : {
      "wikipedia_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9" : 4
    },

This can be used with the next query's pagingSpec:

 {
   "queryType": "select",
   "dataSource": "wikipedia",
   "dimensions":[],
   "metrics":[],
   "granularity": "all",
   "intervals": [
     "2013-01-01/2013-01-02"
   ],
   "pagingSpec":{"pagingIdentifiers": {"wikipedia_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9" : 5}, "threshold":5}
      
 }

Note that in the second query, an offset is specified and that it is 1 greater than the largest offset found in the initial results. To return the next "page", this offset must be incremented by 1 (should be decremented by 1 for descending query), with each new query. When an empty results set is received, the very last page has been returned.